<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .root{
            display: flex;
            width: 90%;
            height: 100px;
            background-color: pink;
        }
       .root div:nth-child(1){
            width: 100px;
            height: 100px;
            background-color: rgb(0, 0, 0);
        }
        .root div:nth-child(2){
            flex: 1;
            background-color: rgb(87, 15, 15);
        }
        .root div:nth-child(3){
            width: 100px;
            height: 100px;
            background-color: rgb(0, 0, 0);
        }
    </style>
</head>
<body>
    <div class="root"> 
        <div>1</div>
        <div>2</div>
        <div>3</div>
    </div>
    
    
</body>
</html>